1. Field of the Invention
This invention relates generally to the field of mattresses, pads and cushions made of resilient synthetic foam and in particular is directed to an improved method for making the same by a novel continuous rotary process.
2. Background of the Invention
Synthetic foam has been widely used to make mattress overlay pads and similar articles intended to cushion the body of a person resting on a supporting surface. In general, such pads seek to provide controlled support by conforming to the natural contours of the user's anatomy so as to avoid areas of concentrated pressure. These areas diminish the user's comfort, and if allowed to persist, the diminished blood flow through the affected tissues frequently leads to painful and slow healing skin ulcerations, which are particularly common among the bed ridden and persons confined to a wheel chair.
Considerable effort has been expended to improve the distribution of pressure over the user's anatomy and provide air flow under the person's body to avoid excessive concentration of heat and humidity which is detrimental to comfort and well being. Many different convoluted pad geometries have been developed as a result. Such pads commonly have a convoluted surface with protuberances arranged in a regular pattern and separated by depressions, so as to afford ventilation underneath the users' body while the protuberances serve as individually compressible cushions capable of responding to varying local pressure over the pad surface. One early configuration was the "egg crate" convoluted pad, in which the supporting surface was dimpled with rounded peaks and depressions in a checkerboard pattern. The convoluted surface is formed by passing a rectangular slab of synthetic foam through a convoluter machine which has a pair of rollers with opposed spaced projecting members arranged in a pattern corresponding to the geometry of the convoluted surface. As the pad passes between and is compressed by the rollers, the pad is sliced by a blade or saw in a transverse plane midway between the rollers. The result is a pair of convoluted pads each having a dimpled surface created by the cutting of the selectively compressed slab. The geometry of the dimpled surface obtainable by this method is limited in that the convoluted surface generally has a sinuous configuration. The elevations as well as the depressions have continuous curvature, and the elevations on the convoluted surface tend to come to a rounded or pointed peak. In many cases this geometry is undesirable in that the peaks tend to concentrate pressure on the body of the person resting on the pad with adverse consequences to blood circulation in the skin and underlying soft tissue. If soft foam is employed to alleviate this problem, the peaks tend to flatten and do not provide sufficient support.
Convoluter machines form two complementary convoluted surfaces simultaneously by slicing a single foam slab lengthwise between the rollers of the convoluting machine. That is, the body support surfaces of the resulting pads are created by slicing in half the foam slab, and no part of these support surfaces existed in the original slab. The result is that the depressions on one pad are formed by slicing away foam which becomes a projection on the other pad, the projections of each pad thus mating into the depressions of the other pad. Consequently, the convoluted surface is equally divided between the raised areas and the depressions, limiting the support provided by the projections which may tend to flatten more easily than is desirable for effective body support. Some of these shortcomings are addressed by Spann in U.S. Pat. No. 4,603,445 which obtains flat topped elevations on convoluted pads in a convoluter roller machine.
Alternative methods of making foam pads exist which avoid these difficulties. One such alternative approach, exemplified by U.S. Pat. No. 4,901,387 issued to Luke, is to saw a foam slab with a computer controlled foam saw machine in which the saw blade spans the width of the foam slab, and the blade moves vertically and horizontally and tilts as needed to cut out the desired contour of the convoluted pad surface, usually by cutting channels which define geometric blocks with flat top surfaces. This method is relatively slow, and is limited to relatively simple geometries of the foam pad supporting surface.
A second alternative method of making support pads, used by Forster in U.S. Pat. No. 4,383,342, is by injecting the foam into a mold cavity. While a wide variety of foam pad surface geometries can be obtained by this method, a rather complex foam injection machine is required and the foam must be formed in the mold cavity from precursor chemicals, so that the process involves both the making of the foam as well as the shaping of the pad, which occur simultaneously.
What is needed is a method and apparatus which retains the simplicity and continuity of operation of the convoluter machine, but overcomes the limitations of the prior art to allow production of convoluted pads with a wide range of possible geometric shapes of the raised portions of the convoluted surface including flat tops on the raised areas, and channels or depressions of arbitrary width between the raised areas of the support surface.